1. Field of the Invention
This invention relates to the preparation of ureteral stents from biodegradable polymers of lactic acid.
2. Description of the Prior Art
Ureteral stents are often used to maintain fluid drainage from the renal pelvis to the bladder when the ureter is obstructed or otherwise impaired, and also for providing support to a collapsed or restricted ureter.
Very often, ureteral stents are positioned in a patient on a temporary basis to provide drainage from the kidney to the bladder following surgery. The stent is generally coiled or looped at opposite ends to prevent upward or downward migration from a predetermined position in the ureter caused by peristaltic action or other body motion that would impose forces on the stent to move it from its predetermined position.
Certain ureteral stents have the capability of infusing fluids into the kidney and are commonly referred to as "infusion stents".
In many situations where the ureteral stent is installed for short term usage, an additional surgical procedure must be employed to remove the stent after its purpose has been fulfilled.
A ureteral stent that is made of a biodegradable and biocompatible material would assure its safe and innocuous disappearance without the need for a second surgical procedure for its removal after it has completed its function.
Canadian Patent No. 808,731 to Fouty discloses the preparation of high molecular weight polylactides with an anionic coordination catalyst containing a divalent metal of Group II of the Periodic Table, to produce a polymer containing the divalent metal as part of the polylactide. Either optical isomer of lactide may be used, and the lactide can be copolymerized with other cyclic esters having from 6 to 8 carbon atoms in the ring, such as glycolide or tetramethyl glycolide.
U.S. Pat. No. 4,045,418 to Sinclair discloses thermally stable copolymers of optically inactive lactide and epsilon caprolactone with a tin ester of carboxylic acid serving as a catalyst to produce throwaway thermoplastic objects that are environmentally attractive because they slowly degrade to harmless substances. Cyclic esters such as glycolide, lactide and the lactones are also disclosed as being used to produce thermoplastics. U.S. Pat. No. 4,057,537 also to Sinclair discloses the copolymerization of glycolide with lactide and various lactones to form copolymers which are reported as useful in making absorbable sutures. Sinclair's primary objective is to produce a non-gummy, high impact, non-brittle, thermally stable copolymer of an optically active lactide and epsilon-caprolactone which can be fabricated into various thermoplastic objects that are disposable and environmentally attractive since they degrade into harmless substances.
U.S. Pat. No. 3,844,987 to Clendinning et al, discloses shaped containers fabricated from biodegradable thermoplastic oxyalkanoyl polymers, such as epsilon-caprolactone polymers, and naturally occurring biodegradable substances to serve as containers in which to germinate and grow seed or seedlings.
U.S. Pat. No. 3,636,956 to Schneider discloses copolymers of L(-)lactide with up to 35% glycolide for use in surgical applications such as sutures and ligatures. U.S. Pat. No. 3,739,773 to Schmitt et al, discloses polyglycolic acid or polyhydroxyacetic ester can be surgically used for a solid prosthesis or a protective gauze and is absorbable by living mammalian tissue.
U.S. Pat. No. 3,736,646 to Schmitt discloses a copolymer containing 15 to 85 mole % of both glycolic and lactic acid can be formed into biodegradable surgical structures such as tubes or sheets or spun as filaments to prepare sutures.
U.S. Pat. No. 4,300,565 to Rosensaft et al, discloses a method for producing sterile surgical articles from a synthetic absorbable copolymer formed by copolymerizing glycolide monomer with a cyclic ester monomer other than a glycolide, such as a lactone, oxalate or carbonate.
U.S. Pat. No. 3,531,561 to Trehu discloses the use of high molecular weight polylactides extruded to form a surgical suture.
U.S. Pat. No. 4,539,981 to Tunc discloses an absorbable bone fixation device made from a polymer of L(-)lactide with an inherent viscosity above 4.5.
U.S. Pat. No. 4,181,983 to Kulkarni discloses an assimilable, porous, hydrophilic prosthesis composed of a polymer of hydroxycarboxylic acid, with the preferred polymer being a lactic acid.
U.S. Pat. No. 4,137,921 to Okuzumi discloses the formation of highly crystalline, fiber-forming addition copolymers of lactide and glycolide having from 50 to 75% glycolide. The lactide-glycolide addition copolymers are highly crystalline and useful in forming fibers for surgical sutures.
U.S. Pat. No. 3,839,927 to Wasserman et al, discloses the formation of a high molecular weight 1-lactide/glycolide copolymer using a stannous octoate catalyst. The copolymer may be extruded to form filaments useable as absorbable sutures.
European Patent Application No. 0204931 to Pertti et al, discloses a synthetic polymeric surgical osteosynthesis material absorbable by the body composed of such polymers as a polylactide.
Other patents of interest relating to the preparation of polylactides include U.S. Pat. Nos. 2,703,316 to Schneider; 2,890,208 to Young et al; 2,362,511 to Teeters; 3,169,945 to Hostettler et al; 3,284,417 to Hostettler et al; 2,758,987 to Salzburg et al and Canadian Patent 779,291 to Kleine.